Ergonomics is the scientific study of man at work. Based on knowledge
of normal human capacity and structure, it is specifically concerned with
the effect on human performance in work of the following factors:

So far, the main application of ergonomics to surgery has been to microsurgery,
because of the critical nature of fine perception and movement control
needed, beyond normal unaided human capacity. The range of possible applications
to the mainstream of general surgery is so wide and detailed that parts
of it can only be outlined briefly in the space available.

30.1 Hand grips

There are five main classes of hand grip used by surgeons:
(1) power grip, for holding large instruments with strength;
(2) external precision grip, as in writing. The instrument is at an angle
of about 45 degrees to the working surface;
(3) internal precision grip, the common scalpel grip in general surgery.
The instrument is practically parallel to the work surface. A variant
is used for scissors and ring-handled tools ;
(4) pinch grip, inappropriately termed the `precision grip' by anthropologists
and orthopaedic surgeons, for picking up small objects;
(5) ulnar storage grip, used for tucking instruments into the palm by
the ring and little fingers, while the remaining digits carry out some
other more ac-curate function. This is an element of several important
double grips of the hand useful in dissecting and suturing, which are
discussed below more fully.

Simple armchair consideration of the power grip provides about a dozen
criteria for handles to fit within it. The more important are a length
greater than palm width of about 12 cm, diameter of 2-3 cm to maximize
skin contact area, slight flattening to control rotation without friction,
flattened areas for the thumb and index for more sensitive tilt control,
avoidance of sharp projections which inhibit voluntary grip strength,
a small pommel and hilt to prevent slip when muscles acting on the hand
relax a little, and a bend, perhaps 30 degrees, where the handle joins
the shaft, to avoid ulnar deviation of the user's wrist for long periods
of time.

This simple check-list helps select from alternatives available those
handle designs best suited for noo' use.
At the opposite extreme, study of the `external precision grip' of the
hand gives a basis for rational design of the microsurgical needleholder
described by Vickers. Based on the features of this hand grip. the handle
requirements are a length over 12 cm. cylindrical. shape about 1 cm in
diameter at the fingertip pulp - much thinner at the thumb cleft, and
a closing pressure fo the for the fingertips of about 50 g wt, above which
normal hand tremor becomes exaggerated.

The impact of this type of detailed analysis has been taken beyond the
operator-instrument interface (the subject of ergonomics) to the instrument-tissue
interface and interfaces within equipment. Vickers has elaborated further
design criteria in this case, such as offset concavo-convex jaws, all
based on a finely detailed consideration of surgical work.

Quite apart from handle design, hand grips and function deserve study
because so much of the surgeon's work is holding tissue, peeling, and
using probes, dissectors and scissors. Three examples follow.

Non-rigid tissue is best cut at right-angles to lines of tension, requiring
two pulling forces, or a second re-action. A double hand grip by the operator
allows him to stretch tissue in one hand while cutting it with excellent
control with the other (Figure 30.1).

Figure 30.1 Mechanism of using double hand grip to stretch tissue in order to cut under control

Figure 30.2 Maintenance of desired tension on suture during procedure of suturing

A second example is the looping of a continuous suture from the tissue
over the dorsum of the ring finger and under the palmar aspect of the
flexed middle finger like a woman knitting. This lets the operator maintain
the exact tension he wants on the suture while leaving the thumb and index
finger free to pout open the tissue edges with-out needing an assistant,
or to use dissecting forceps while holding the tissue edges apart with
the bulk of his hand (Figure 30.2).

Dissecting a hollow adherent structure such as some hernial sacs, a difficult
duodenal stump, or a gall bladder, is also simplified by a double hand
grip in which the structure is tensed over the index tip, which provides
very accurate information about the thickness of the layer being created,
and the presence of intervening structures (Figure 30.3).

30.2 Workplace layout and organization

The best method of achieving efficient work organization is by many repetitions
of a procedure, with gradual evolution of improvements. The same operating
team carrying out many hip replacements or cleft palate repairs will achieve
a rhythm of work impossible with changing staff and infrequent procedures.
However, much can be achieved by learning, from industrial examples in
textbooks of work study, and attending to several practical factors whose
nature ranges from the very general to the detailed.
(1) Sympathetic competent leadership for example, and patience.

Repeatedly similar technique. Rehearsal of complicated new procedures.
Up-to-date cards of instruments and sutures used and special requirements
for each procedure. The minimum of gadgetry for its own sake, and simplification
of operative technique.

Attention to equipment placement and movement. based on envelopes of
reach for the arm. forceps racks designed by Sir Heneage Oglivie in 1939,
and the `drop-passage' of instruments described by H.A.F. Dudley in the
standard work Operative Surgery.
Operator seating, arm support, and operating table design remain problems
still managed by flair and in-tuition instead of scientific analysis,
despite a wealth of practical guidelines in the ergonomic literature.
With concepts already available, their application awaits only the interest
and energy of some young surgeons. It is easier for a surgeon to learn
ergonomics than for an ergonomist to learn enough surgery to bridge the
gap between the two disciplines.

30.3 Environmental conditionslighting and vision

Studies in factories have shown the effect of environmental conditions
on productivity, which is highest at a working temperature of about 18
°C, measurable humidity, and little noise. Lighting is one of the
main factors which determines visual acuity and perception, and is a good
example of an environmental factor to analyse for surgical work. Acuity
depends on:

(1) Lighting intensity: within broad limits, visual acuity is proportional
to the logarithm of the lighting intensity. Surgeons should recognize
the difference between 200lx,.for desk work, and 3000 lx for an abdominal
operation. Outside the operative field, the theatre sister has a problem
with relatively dull lighting, especially in picking out one of several
similar instruments. (There are labelling implications here.)

(2) Glare: this decreases acuity the closer is its line of incidence to
the line of sight, and the brighter it is. Matt or satin finish of instruments
is an advantage, though less corrosion resistant and harder to keep clean.
Green drapes were introduced by Lord Moynihan early this century for such
reasons, but they mask cyanosis for the anaesthetist, who now needs a
white undersheet to observe the patient's colour.

(3) Colour contrast: common examples are the use of the tourniquet, methylene
blue, and the attempt to use vital staining of tissues (most recently
with fluorescent dyes under the operating microscope) to help discriminate
structures. As in many other situations, technology is less useful than experience,
but a help in its absence.

(4) Other factors important for seeing fine detail include binocularity,
visual health, trained and experienced perception, magnification, the
moulding effect of directional lighting, colour rendering according to
the colour temperature of the light source, filters, and reflectors, flicker,
and unwanted effects such as heating. Lighting levels should in-crease
in proportion to magnification. A total approach would consider the ergonomics
of light positioning and controls.

30.4 Skill acquisition

The manual skills of surgeons can be studied in the same way as skills
in sport, industry or music. The process of skill acquisition has been
divided by Glencross, at Flinders University, into three stages. Coding,
the first stage, is learning to relate a particular movement to a particular
end result, such as pressing middle C on the piano, or squeezing an instrument
or tissue with a given amount of force. The second stage of temporal organization
is the arrangement of coded movements into a sequence, such as the notes
of a melody or tying a surgical knot, perhaps under the microscope. In
the final stage of hierarchical organization, there is a 'pro-gramme'
or `sub-routine' ready to be called on by the operator, with preliminary
modifications according to other sensory input or processing, but which
cannot be interrupted halfway through. It gives a smooth and rhythmic
performance economical in time, if it does not have to be repeated. This
is a constant feature of the skills of the best workers, artists and sportsmen.

30.5 Future developments and implications

By their temperament and training, surgeons are well equipped to make
practical use of the rich existing fund of ergonomic knowledge, aided
by new habits of observation concentrating on the operator and his hands
and eyes, instead of on the patient, and by the use of video-tape technology
now readily available. Only the stimulus for such work has been missing
up till now. The application of ergonomics, in the correct context of
surgical pathology, should result in better handiwork at operation, more
satisfaction and less worry for the operator, and a better result for
the patient.